The present invention relates generally to medical devices for detecting cardiac disease. More particularly, the present invention relates to medical devices for detecting vulnerable plaque within a blood vessel.
Therapy modalities for heart disease have traditionally focused on treating blood vessels which have become occluded (blocked) or stenotic (narrowed) by calcified plaque deposits. Blood vessels which have become occluded or stenotic in this manner may interrupt the blood flow which supplies oxygen to the heart muscle. Occluded or stenotic blood vessels may be treated with a number of medical procedures including angioplasty and atherectomy. Angioplasty techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) are relatively noninvasive methods of treating restrictions in blood vessels. In these procedures, a balloon catheter is advanced over a guidewire until the balloon is positioned proximate to a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is stretched. During an atherectomy procedure, the stenotic lesion is mechanically cut or abraded away from the blood vessel wall using an atherectomy catheter.
Calcified plaque deposits typically comprise hard materials. But, plaque may also comprise soft materials or combinations of soft and hard materials. Soft plague typically comprises deposits of cholesterol and other fats which build up within the blood vessels as a patient ages. The build up of plaque in the blood vessels is sometimes referred to as atherosclerosis, or hardening of the arteries.
Atherosclerosis often begins as a small injury to an artery wall. This injury triggers a cascade of injury and response, inflammation, and healing, which may ultimately lead to the narrowing of the artery. As the atherosclerotic plaque worsens, inflammatory cells, especially macrophages, collect, at the site to isolate, the debris of the damaged tissue. The result is a core of lipid, macrophages or foam cells and nectrotic tissue, covered by a thin fibrous cap of scar tissue. If the fibrous cap becomes weakened or is subjected to excessive mechanical stress, it may rupture, exposing the thrombogenic damaged endothelium and metabolic byproducts to the blood stream. If the resulting blood clot is severe enough, it may occlude the artery. If this obstruction persists in a coronary artery, a myocardial infarction or angina may result.
Plaque deposits which are at risk of rupturing are sometimes referred to as vulnerable plaque. Vulnerable plaque typically comprises a core of soft materials covered with a fibrous cap. Many vulnerable plaque deposits do not limit the flow of blood through the blood vessels. It has recently been appreciated that vulnerable plaques which do not limit flow may be particularly dangerous because they can rupture suddenly causing heart attack and death. This may occur, for example, when the vulnerable plaque ruptures and a blood clot is formed inside the blood vessel lumen causing a blockage.
Recently, the pivotal role of inflammation in the progression of atherosclerosis has been recognized. A systemic increase in temperature is often associated with infection (e.g., a fever). Likewise, a local infection or localized damage to tissue may result in a localized increase in temperature. An increase in temperature is thought to be caused by the response of the immune system to infection, known as inflammation and an increase in metabolic activity involved in the healing process. It has been observed that the inflamed necrotic core of a vulnerable plaque maintains itself at a temperature which may be one or more degrees Celsius higher than the surrounding tissue. For example, an inflamed plaque in a human heart, where the normal temperature is about 37xc2x0 C. may be at a temperature as high as 40xc2x0 C.
The present invention relates generally to medical devices for detecting cardiac disease. More particularly, the present invention relates to medical devices for detecting vulnerable plaque within a blood vessel. A catheter in accordance with one embodiment of the present invention includes an elongate shaft and a plurality of arms fixed to the elongate shaft.
The arms preferably have an extended position and a retracted position. A sensor is fixed to each arm proximate a first end thereof. In a preferred embodiment, each sensor contacts the inner surface of a blood vessel when the arms are in the extended position. In a preferred embodiment, a sheath is disposed about the elongate shaft. The arms may be urged into the retracted position by advancing the sheath distally along the elongate shaft.
The signal from each sensor may be displayed and/or recorded using a suitable instrument. Variations in these signals may be noted as the catheter is moved proximally and/or distally-through the blood vessel thermally mapping the transversed region. The variations in the sensor signal may be correlated with the axial position of the catheter. This information may be used to identify the position of any vulnerable plaque deposits in the blood vessel.
In a preferred embodiment, the arms of the catheter expand radially away from the elongate shaft. The angular orientation of plaque deposits within the blood vessel may be identified by observing variations between the signals from the different sensors. For example, sensors which are proximate to vulnerable plaque deposits may read higher temperatures than sensors which are not proximate to vulnerable plaque deposits.
A catheter in accordance with an additional embodiment of the present invention includes one arm comprising a spring which is biased to assume an extended position. A sensor is fixed to the arm proximate a first end thereof. This catheter may also be used for mapping the locations of vulnerable plaque deposits within a blood vessel.
In a preferred embodiment, the sensor contacts the inner surface of the blood vessel when the arm is in the extended position. In this preferred embodiment, the temperature measured by the sensor may rise when the sensor is proximate to a vulnerable plaque deposit. Variations in the temperature measured by the sensor may be noted as the catheter is moved proximally and/or distally through the blood vessel, and these variations may be correlated to the axial position of vulnerable plaque deposits.
Variations in the signal from the sensor may also be noted as the catheter is rotated about it""s longitudinal axis. These variations may be correlated to the angular location of vulnerable plaque deposits within the blood vessel.
Yet another exemplary embodiment of a catheter in accordance with the present invention includes a body member disposed about an elongate shaft of the catheter. The body member defines a plurality of flow channels and a temperature sensor is disposed within each channel. This catheter may also be used along with methods in accordance with the present invention for mapping the locations of vulnerable plaque deposits within the blood vessel.
The body member of the catheter is preferably sized so that an outer surface of the body member is disposed proximate the inner surface of the blood vessel. When this is the case, blood flowing proximate the inner surface of the blood vessel will flow into the channels. Sensors may be used to measure the temperature of the blood flowing through the channels. Blood which flows over a vulnerable plaque deposit will be warmed by the vulnerable plaque deposit. The increased temperature of this blood may be observed and/or recorded using the sensors disposed within the channels.
As the catheter is moved proximally and/or distally through the blood vessel, the distal end of the body member will be proximate different portions of the inner surface of the blood vessel. Variations in the signals from the sensors may be noted as the catheter is moved proximally and/or distally through the blood vessel, and these variations may be correlated to the axial position of the catheter. This information may be used to identify an axial component of the position of any vulnerable plaque deposits in the blood vessel.
The flow channels and the sensors are preferably disposed radially about the elongate shaft. An angular component of the position of plaque deposits within the blood vessel may be identified by observing variations between the signals from the different sensors. For example, sensors which are proximate vulnerable plaque deposits may read higher temperatures than sensors which are not proximate vulnerable plaque deposits.